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Quenching Studies (quenching + studies)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Electrochemical Quartz Crystal Impedance and Fluorescence Quenching Studies on the Binding of Carbon Nanotubes (CNTs)-Adsorbed and Solution Rutin with Hemoglobin

BIOTECHNOLOGY PROGRESS, Issue 2 2007
Yuhua Su
Electrochemical quartz crystal impedance (QCI) technique was utilized to monitor in situ the adsorption of rutin (RT) onto a carbon nanotubes (CNTs)-modified gold electrode and to study the binding process of solution hemoglobin (Hb) to RT immobilized on the electrode. Time courses of the QCI parameters including crystal resonant frequency were simultaneously obtained during the RT adsorption and Hb-RT binding. In contrast to the negligible RT adsorption at a bare gold electrode, the modification by CNTs notably enhanced the amount of adsorption, and almost all of the adsorbed RT molecules were found to be electroactive. On the basis of the frequency response from the binding of adsorbed RT to solution Hb and the diminished electroactivity of adsorbed RT after the formation of the electrochemically inactive RT-Hb adduct, the average binding molar ratio of adsorbed RT to Hb was estimated to be 23.9:1, and the association constant (Ka) for the binding was estimated to be 2.87 × 106 (frequency) and 3.92 × 106 (charge) L mol,1, respectively. Comparable results were obtained from fluorescence quenching measurements in mixed solutions containing RT of fixed concentration and Hb of varying concentrations, demonstrating that the interfacial RT here behaved equivalently in the RT-Hb binding activity compared to that in solution. This work may have presented a new and general protocol involving CNTs to study many other electroactive natural antioxidants or drugs that are at the interface or in solution, their binding with proteins or other biomolecules, and changes of their antioxidant activity after the binding. [source]

Photoinduced Electron Transfer Reactions by SmI2 in THF: Luminescence Quenching Studies and Mechanistic Investigations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005
Edamana Prasad Dr.
Abstract Photoluminescence quenching studies of SmI2 in dry THF were carried out in the presence of five different classes of compounds: ketone, alkyl chloride, nitrile, alkene and imine. The free energy change (,G,0) of the photoinduced electron transfer (PET) reactions was calculated from the redox potentials of the donor (SmI2) and acceptors. The bimolecular quenching constants (kq) derived from the Stern,Volmer experiments parallel the free energy changes of the PET processes. The observed quenching constants were compared with the theoretically derived electron transfer rate constants (ket) from Marcus theory and found to be in good agreement when a value of ,=167 kJ,mol,1 (40 kcal,mol,1) was used for the reorganization energy of the system. A careful comparison of the excited state dynamics of SmII in the solid state to the results obtained in solution (THF) provides new insight in to the excited states of SmII in THF. The activation parameters determined for the PET reactions in SmI2/1-chlorobutane system are consistent with a less ordered transition state and high degree of bond reorganization in the activated complex compared to similar ground state reactions. Irradiation studies clearly show that SmI2 acts as a better reductant in the excited state and provides an alternative pathway for rate enhancement in known and novel functional group reductions. [source]

Parallel and antiparallel dimers of magainin 2: their interaction with phospholipid membrane and antibacterial activity

JOURNAL OF PEPTIDE SCIENCE, Issue 10 2002
Yasuhiro Mukai
Abstract Magainin 2 (M2) forms pores by associating with several other M2 molecules in lipid membranes and shows antibacterial activity. To examine the effect of M2 dimerization on biological activity and membrane interaction, parallel and antiparallel M2 dimers were prepared from two monomeric precursors. Antibacterial and haemolytic activities were enhanced by dimerization. CD measurements showed that both dimers and monomers have an ,-helical structure in the presence of lipid vesicles. Tryptophan fluorescence shift and KI quenching studies showed that all the peptides were more deeply embedded in acidic liposomes than in neutral liposomes. Experiments on dye-leakage activity and membrane translocation of peptides suggest that dimers and monomers form pores through lipid membranes, although the pore formation may be accompanied by membrane disturbance. Although dimerization of M2 increased the interaction activity with lipid membranes, no appreciable difference between the activities of parallel and antiparallel M2 dimers was observed. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source]